A conventional variable valve operating device is known, as disclosed, for example, in Japanese Patent Laid-open No. 2003-239712, in which the valve lift amount and valve timing are mechanically changed according to engine operating conditions. In the variable valve operating device (hereinafter referred to as prior art) disclosed in Japanese Patent Laid-open No. 2003-239712, a control arm is fixed to a control shaft disposed in parallel with a camshaft and one end portion of a follower is mounted on the control arm and allowed to swing freely. Further, a swing cam is mounted on the control shaft and allowed to swing freely. A rocker arm is pressed against a cam surface of the swing cam. A first roller and a second roller that are rotatable mutually independently of each other are coaxially mounted on the follower. The first roller abuts against a valve cam of the camshaft. The second roller abuts against a flat surface (abutment surface) of the swing cam formed on a side opposite to the swing cam surface.
According to these arrangements, a rotational position of the control arm is changed through rotation of the control shaft. This displaces the follower to thereby change the distance between the control shaft and the point of abutment between the swing cam and the second roller, whereby the valve lift amount is changed. This also changes a circumferential position of the valve cam that abuts on the first roller at the same rotational angular position of the camshaft, which results in the valve timing being changed. Specifically, according to the prior art disclosed in Japanese Patent Laid-open No. 2003-239712, the valve lift amount and valve timing can be changed simultaneously by controlling the rotation position of the control shaft using a motor.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.
[Patent Document 1]
Japanese Patent Laid-open No. 2003-239712
[Patent Document 2]
Japanese Patent Laid-open No. Hei 7-63023
[Patent Document 3]
Japanese Patent Laid-open No. 2002-371816
[Patent Document 4]
Japanese Patent Laid-open No. 2004-108302